1. Field of the Invention:
The present invention relates to a Planar Inverted F-Antenna (PIFA), and in particular, to a single feed, multi band (Three, four or five band) PIFA whose radiating/receiving element contains one or more slots.
2. Description of Related Art:
With the rapid progress of cellular communication and the increasing demand for multi systems application, there is a trend toward the design of multi purpose, multi band, cellular handsets, i.e. cellular wireless communications devices.
This demand has advanced from two band cellular antennas to three band antennas that cover the lower US or European cellular band, as well as the digital calling selecting (DCS) and personal communication service (PCS) bands.
It is reasonable to foresee a future requirement for a single antenna that covers the AMPS/PCS and GSM/DCS bands for global cellular communications (wherein AMPS stands for advanced mobile phone service, also called North American cellular phone system, and wherein GSM stands for global system for mobile communications).
There is also a desire to use cellular antennas that are internal to a wireless communication device such as a cellular handset. Since an internal antenna is integrated into, or buried within, the wireless communication device, an internal antenna eliminates any antenna element that protrudes outward from the body of the wireless communication device.
Internal antennas have several advantages, such as being less prone to damage, a reduction in the size of the handset, and increased portability of the handset. When an internal antenna is provided, the wireless communication device""s printed circuit board may also serve as a ground plane element for the internal antenna.
Among the choices that are available for internal antennas, a planar inverted-F antenna (PIFA) has great promise. PIFAs have many distinguishing properties, such as being relative lightweight, ease of adaptation and integration into the wireless communication device""s chassis, a moderate range of bandwidth, omni directional radiation patterns in orthogonal principal planes for vertical polarization, versatility for optimization, and arrangements to achieve size reduction. The sensitivity of PIFAs to both vertical and horizontal polarization is of practical importance in mobile cellular/RF data communication applications due to the absence of a requirement for a fixed orientation of the antenna, as well as multi path propagation conditions. All of these features make a PIFA a good choice for use as an internal antenna for mobile cellular/RF data communication applications.
In the past, success has been achieved in the design of a single feed PIFA having two resonant frequencies, this resulting in a two band PIFA. In view of the inherent bandwidth limitations that are associated with conventional PIFA designs, most of the prior art single feed, two band, PIFAs exhibit useful and desirable performance that covers only two cellular frequency bands.
U.S. Pat. No. 5,926,139 (incorporated herein by reference), and a paper by Liu. et. al. entitled xe2x80x9cDual Frequency Planar Invertedxe2x80x94F Antennaxe2x80x9d, IEEE Trans. Antenna and Propagation, Vol. AP-45, No. 10, pp. 1451-1548, Oct. 1997, are examples of the prior single feed, dual band, PIFAs.
FIGS. 6a and 6b illustrate a prior art single feed, two band, PIFA 50. Dual band PIFA 50 that includes a radiating/receiving element 301 (hereinafter radiating element) and a ground plane 302. An L-shaped open slot 303 within radiating element 301 provides quasi-physical partitioning of radiating element 301.
The portion of radiating element 301 having the dimensions of length L1 and width W1 resonates at the lower frequency band of the PIFA""s dual band operation. The portion of radiating element 301 having the dimensions of length L2 and width W2 resonates at the upper frequency band of the dual band operation.
A power feedhole 304 is located in radiating element 301, and a connector feed pin 305 that feeds radio frequency (RF) power to radiating element 301 is inserted through feedhole 304 from the bottom surface of ground plane 302. Connector feed pin 305 is electrically insulated from ground plane 302 at the point where feed pin 305 passes through a hole that is provided in ground plane 302. Connector feed pin 305 is electrically connected to radiating element 301 at 306.
The outer body portion 314 of the connector that includes feed pin 305 is connected to ground plane 302 at 307, and feed pin 305 is electrically insulated from the outer body portion 314 of this connector.
A hole 308 is provided in radiating element 301, and a conductive post or pin 309 which provides a short circuit between radiating element 301 and ground plane 302 is inserted through hole 308. Conductive post 309 is connected to radiating element 301 at 310, and is connected to ground plane 302 at 311.
Dual band impedance matching of radiating element 301 is determined by the diameter of connector feed pin 305, by the diameter of conductive shorting post 309, and by the separation distance that exists between connector feed pin 305 and conductive shorting post 309.
A disadvantage of the dual band PIFA 50 illustrated in FIGS. 6a and 6b is the lack of a simple means of adjusting the frequency separation between the antenna""s lower and the upper resonant frequency bands. A change in the frequency separation of these two resonant frequency bands requires the repositioning of an L-shaped slot 303 that is formed in radiating element 301. PIFA 50 also provides a constraint on a realizable bandwidth that is centered around the two resonant frequencies of PIFA 50.
Techniques for enhancing the bandwidth around the two resonant frequencies of PIFA 50 are of practical importance. Depending upon the bandwidth that is achievable around the two resonant frequencies, dual resonant PIFA 50 may potentially cover more than two frequency bands.
For the design of a dual band (i.e. a dual resonance) PIFA that covers the AMPS/PCS and the GSM/DCS bands for global cellular communications, the bandwidth requirement of the lower resonance of a PIFA that covers both the AMPS and the GSM bands is about 15.29%, when compared to about 8.15% for the AMPS band only. Likewise, the bandwidth requirement of the upper resonance of a PIFA that covers both the DCS and PCS bands is about 15.14%, as compared to about 7.29% required for the PCS band only.
Attempts have been made to improve the bandwidth centered around the upper resonant frequency of a dual band PIFA in order to realize three or tri band performance that covers three cellular frequency bands.
Simultaneously enhancing the bandwidth centered around the two resonant frequencies of a dual band cellular PIFA in order to accomplish the four or quad band operation that is essential for global cellular coverage or applications is not known.
Therefore, a single feed, four band, PIFA comprising the four basic frequency bands of global cellular communication is needed by the art, and such a single feed, quad band, PIFA is of practical importance for the emerging trend of a single cellular handset for global cellular coverage.
In order to keep pace with another category of recent advance in cellular communications, there is a requirement for a single antenna that simultaneously covers both cellular and non-cellular applications, examples of non-cellular applications being global positioning system (GPS) and Bluetooth (BT) (wherein Bluetooth is a code name for a proposed open specification to standardize data synchronization between disparate PC and handheld PC devices).
System applications like GPS and BT or IEEE 802.11 have frequency bands that are significantly off of the dual cellular bands of AMPS/GSM and DCS/PCS. An inherent problem is the bandwidth requirement for the upper resonant band of an antenna to simultaneously cover the upper cellular (DCS or PCS) frequencies and the non-cellular (GPS or BT) frequencies.
Enhancing the bandwidth of a cellular, dual band, PIFA to additionally cover GPS and BT applications is difficult. Extension of currently available cellular dual band PIFAs to additionally cover the GPS and the BT frequency bands requires a rather non-realizable bandwidth that is centered around these two cellular frequencies. For example, extending the operation of a cellular, dual band (AMPS/PCS), PIFA to cover the GPS band implies a bandwidth requirement of about 23.35% for the GPS/PCS bands (1575 to 1990 MHz), and the corresponding bandwidth requirement to cover the GPS/DCS bands (1575 to 1880 MHz) is about 17.72%.
Extending the operation of a cellular, dual band (AMPS/PCS), PIFA to cover the industrial scientific medical (ISM) band requires a bandwidth of about 29.89% for the PCS/ISM bands (1850 to 2500 MHz). It is difficult to achieve such a wide bandwidth using known single feed, dual band, PIFAs.
The present invention provides single feed, three band, four band and five band, PIFAs for simultaneous cellular and non-cellular applications.
A single feed, three band, PIFA for both cellular and non-cellular (GPS or ISM) applications is described in above-referenced U.S. Pat. disclosure Ser. No. 10/135,312. In the above-referenced patent application, a third resonant frequency of the PIFA is provided by a shorted parasitic element that is placed between the PIFA""s radiating element and the ground plane. This parasitic element is placed internal to a dual cellular band PIFA in order to provide a third and exclusively non-cellular resonant frequency band for the PIFA. While this referenced patent application deals with a three band (two cellular bands and one non-cellular band) PIFA, the present invention deals with a single feed, four band, (two cellular bands and two non-cellular bands) PIFA, or a single feed, five band (three cellular bands and two non-cellular bands), PIFA, wherein the PIFAs overcome the enormity of the bandwidth requirement that the PIFA""s upper resonant frequency band should simultaneously cover both the upper cellular frequency and the upper non-cellular frequency.
Embodiments of single feed, multi band, PIFAs (for both Cellular and Non-cellular applications) in accordance with this invention include:
(a) A combined L-shaped slot and annular slot for four band operation (four cellular bands), see FIGS. 1a, 1b, 1c, 2a, 2b and 2c. 
(b) Two generally L-shaped slots and one generally C-shaped slot for five band operation (three cellular bands and two non-cellular bands), see FIGS. 3a, 3b and 3c. 
(c) A single annular slot for three band operation (two cellular bands and one non-cellular band), see FIGS. 4a and 4b. 
(d) Two annular slots for four band operation (two cellular bands and two non-cellular bands), see FIGS. 5a and 5b. 
Single feed, multi band, PIFAs of the present invention which provide for the simultaneous inclusion of both cellular and non-cellular resonant bands do not require an increase in the overall physical size or volume of the PIFAs, and therefore provide a desirable feature of compactness, despite the PIFA""s multi band operational capability.
This invention provides PIFA embodiments having a single feed and having three, four or five frequency band operation.
Multiple frequency PIFAs in accordance with this invention include a variety of combinations that are useful for many systems application. Multi frequency operation of a single feed PIFA in accordance with this invention include, but are not limited to:
(a) Four band for global cellular coverage (i.e. AMPS/PCS/GSM/DCS), see FIGS. 1a, 1b, 1c, 2a, 2b and 2c. 
(b) Five band for three cellular band coverage and two non cellular band coverage (i.e. AMPS/DCS/PCS cellular or GSM/DCS/PCS cellular and GPS/ISM or GPS/BT non-cellular), see FIGS. 3a, 3b and 3c. 
(c) Three band for two cellular band coverage and one non cellular band coverage (i.e. AMPS/PCS or GSM/DCS and GPS or BT), see FIGS. 4a and 4b. 
(d) Four band for two cellular band coverage and two non cellular band coverage (i.e. AMPS/PCS or GSM/DCS and GPS/ISM or GPS/BT), see FIGS. 5a and 5b. 
A single feed, four band (AMPS/GSM/DCS/PCS cellular bands), PIFA forms the first embodiment of this invention, wherein the four band operation is provided for by the combination of an L-shaped slot with an annular slot, resulting in a composite slot in the radiating element of the PIFA.
Although the use of an L-shaped slot is shown in prior art FIGS. 6a and 6b, the present invention""s advantages that are provided by a required location of the L-shaped slot with respect to the positions of the PIFA""s feed post and shorting post are not offered by the prior art. More specifically, the first embodiment of this invention locates the open end of an L-shaped slot portion between the radiating element""s feed post and shorting post. This location of the open end of the L-shaped slot portion between the feed post (or strip) and the shorting post (or strip) results in two resonant frequency bands having a relatively wide bandwidth that is centered around the two resonant frequencies.
The length of the L-shaped slot portion of this first embodiment provides reactive loading on the resonant frequencies of the PIFA, and as a result the resonant frequencies can be lowered or reduced without increasing the physical size of the PIFA.
In this first embodiment of the invention an annular slot portion having a generally rectangular shape extends generally parallel to the four outer edges of the PIFA""s radiating element, thus forming a generally rectangular inner radiating element and a generally C-shaped main or outer radiating element that surrounds the inner radiating element.
The physical size and the location of the annular slot portion is such that the annular slot portion merges or combines with a horizontal segment of the L-shaped slot portion. That is, the annular slot portion merges or combines with a segment of the L-shaped slot portion that extends generally parallel to the minor or short axis of the PIFA""s ground plane element.
Importantly, a common region of overlap of the two slot portions is in close vicinity of the non radiating edge of the radiating/receiving element that contains the PIFA""s feed strip and shorting strip.
The PIFA""s inner radiating element and outer radiating element are electrically connected by way of a conductive stub that is located within the annular slot portion, and this conductive stub is located in close proximity to the radiating edge of the radiating element, i.e. the edge that is opposite the feed strip and shorting strip. This conductive stub is placed within the annular slot at this location so as to form a tuning element that controls the resonance frequency characteristics of the PIFA""s radiating element.
The PIFA""s resonant frequencies, and the associated bandwidth that is centered around these two resonant frequencies, are determined by the following design parameters:
(a) The position of the shorting strip,
(b) The width of the shorting strip,
(c) The position of the feed strip,
(d) The width of the feed strip,
(e) The location of the open end of the L-shaped slot portion on the non radiating edge of the radiating element, i.e. the edge that contains the shorting strip and feed strip,
(f) The size and width of the segment of the L-shaped slot portion that is parallel to the major or long axis of the ground plane,
(g) The size and location of the annular slot portion,
(h) The location of the conductive stub that electrically connects the inner and outer radiating elements, and
(i) The width of the conductive stub.
Based on a combination of the L-shaped slot portion and the annular slot portion to form a composite slot, as well as the placement of the open end of the L-shaped slot portion between the feed strip and the shorting strip, a single feed, four band (AMPS/GSM/DCS/PCS), PIFA is provided having satisfactory bandwidth. The single feed, four band, PIFA of the first embodiment of this invention provides good gain performance in all the four cellular bands that are required for global coverage. The single feed, four band, PIFA covers the four basic frequency bands of global cellular communication as proposed in the first embodiment of this invention.
The present invention also provides embodiments of a single feed PIFA having three resonant frequencies or four resonant frequencies covering the dual cellular and the GPS or the BT frequencies, as well as two cellular and two non cellular frequencies.
A single feed, five band (three cellular bands and two non-cellular bands, PIFA comprises a second embodiment of the present invention. This second embodiment of the invention provides two L-shaped slots and one C-shaped slot within the PIFA""s radiating element, with the open ends of all of the slots being located on the non radiating edge of the radiating element that contains a shorting strip and a feed strip.
As with the first embodiment of the invention, a first L-shaped slot has its open end located between the feed strip and shorting strip. The open end of the C-shaped slot is located to the other side of the feed strip, and the open end of the second L-shaped slot is located between the open end of the C-shaped slot, and an adjacent side edge of the radiating element.
The positions and the contours of these three slots provide four distinct resonant frequencies for the single feed PIFA of this second embodiment of the invention.
The L-shaped slot that is located between the feed strip and shorting strip provides two distinct resonant bands. The two other slots provide separate resonant frequency bands having distinct resonant frequencies.
Performance of this second embodiment of the invention centered around a first resonance is optimized for the AMPS band. The bandwidth of this second embodiment centered around a third resonance frequency includes the two upper cellular bands DCS and PCS. Thus, a combination of the first and the third resonance frequency of the second embodiment of the invention provides three-cellular band performance.
Similarly, two non-cellular band performance of the second embodiment of the invention is provided by way of the second and a fourth resonance frequency of the PIFA. Specifically, resonance of the PIFA in the lower non-cellular frequency band (GPS) is provided by tuning the second resonant frequency as a function of the position of the second L-shaped slot. The requirement of resonance in the upper non-cellular frequency band (ISM or BT) is provided by optimizing the bandwidth performance centered around the fourth resonant frequency of the PIFA.
The above-mentioned use of two L-shaped slots and one C-shaped slot on a PIFA""s radiating element provides a single feed, five band, PIFA. This single feed, five band, PIFA is provided using concepts that are also utilized in the above-mentioned first embodiment of the invention, and exhibits satisfactory gain and bandwidth at three cellular bands and two non cellular bands.
A single feed, three band, PIFA (two cellular bands and one non cellular band) having a single annular slot forms the third embodiment of the invention wherein the dual resonant cellular frequencies are provided by a radiating element that includes a shorting strip and capacitive loading.
The desired separation between the two cellular frequency bands of the single feed PIFA is initially optimized by varying the position of a shorting strip that is located along the non radiating edge of the radiating element (i.e. the edge that is closest to a corresponding end of the ground plane), and by varying the position of the shorting strip along this non-radiating edge of the radiating element that is parallel to the minor axis of the ground plane element.
Parameters such as the width of the shorting strip, the location of the feed strip, and the size of the shorting strip determine a bandwidth centered around the two resonant frequencies, and these parameters are optimized to provide a dual cellular performance of the PIFA.
Resonance in the non-cellular band, which is distinctly far off from the two cellular bands, constitutes the third resonant frequency of the PIFA, and this third resonant frequency is generated by placement of an annular slot within the radiating element, the annular slot dividing the PIFA""s radiating element into inner and outer radiating elements. Placement of conductive stubs at pre-desired locations within the contour of the annular slot results in the modified C-shaped inner radiating element. Because of the above-mentioned conductive stub, the annular slot transforms to a C-shaped slot.
A conductive stub is placed at a desired location within the annular slot, to electrically connect the inner radiating element to the outer radiating element. The width of the annular slot and the perimeter of the inner radiating element control the bandwidth and the resonant frequency of the third or non-cellular resonance band of the multi band PIFA in accordance with the third embodiment of the invention. In addition, the width and the position of the conductive stub form tuning parameters that control and vary the resonant frequency of the third or non-cellular band of the PIFA.
The width of the annular slot, the perimeter of the annular slot, the location of the annular slot, and the width and the position of the conductive stub that connects the inner radiating element to the outer radiating element, are optimized to provide the third resonance frequency of the PIFA in the non-cellular frequency band.
In a fourth embodiment of this invention the above-described single feed, three band, PIFA having a single annular slot is modified to provide a single feed, four band, PIFA by incorporation two annular slots within the PIFA""s radiating element. This fourth embodiment provides four distinct resonant frequencies for the single feed PIFA, thus simultaneous providing for two cellular bands and two non-cellular bands of operation.
In this fourth embodiment wherein a single feed, four band, PIFA includes two annular slots, a second annular slot is placed within a first annular slot.
As with the above-described three band PIFA of the third embodiment of this invention, the desired bandwidth for the two band cellular performance of the PIFA of the fourth embodiment is accomplished by optimizing parameters such as the dimensions of the radiating element, the height of the PIFA, the location and width of the shorting strip, as well as the location and size of the feed strip.
Resonance of the PIFA in the lower non-cellular frequency band is provided by the first (outer) annular slot. The first annular slot is of a substantially rectangular shape and results in the formation of a generally C-shaped first inner radiating element. The first annular slot also separates the C-shaped first inner radiating element from an outer radiating element. A first conductive stub is placed within the first annular slot to electrically connect the C-shaped first inner radiating element to the outer radiating element.
The width of this first annular slot, and the perimeter of this C-shaped first inner radiating element, control the bandwidth and the resonant frequency of the lower non-cellular resonance of the multi band PIFA of the fourth embodiment. In addition, the width and the position of the first conductive stub that connects the C-shaped first inner radiating element to the outer radiating element form additional tuning parameters that control and vary the resonant frequency of the lower non cellular band of the multi band PIFA.
The width and the perimeter of the first annular slot, the location of the first annular slot, the width and the position of the first conductive stub that connects the C-shaped first inner radiating element to the outer radiating element are parameters that are optimized to obtain the third resonance of the PIFA in the non cellular frequency band.
In the fourth embodiment of the invention, resonance of the multi band PIFA in the upper non-cellular frequency band is provided by a second (inner) annular slot. This second annular slot is of substantially rectangular shape. It is encompassed by the C-shaped first inner radiating element, and it forms a generally rectangular second inner radiating element.
A second conductive stub is placed at within this second annular slot to electrically connect the rectangular second inner radiating element to the C-shaped first inner radiating element. The width of the second annular slot and the perimeter of the C-shaped second inner radiating element control the bandwidth and the resonant frequency of the fourth or upper non cellular resonance band of the multi band PIFA of this fourth embodiment. Placement of a second conductive stub in the second annular slot modifies the rectangular shape of the second inner element to that of a generally C-shape. Because of the above-mentioned second conductive stub, the second annular slot transforms into a second generally C-shaped slot.
In addition, the width and the position of the second conductive stub act as tuning means that control and vary the resonant frequency of the upper non-cellular band of the multi band PIFA of the fourth embodiment of the invention.
Resonance of the multi band PIFA in the upper non cellular frequency band is provided by optimizing parameters such as the width and the perimeter of the second annular slot, the location of the second annular slot, and the width and position of the second conductive stub that connects the C-shaped first inner radiating element to the C-shaped second inner radiating element.
Providing three, four or five band PIFAs in accordance with the various embodiments of this invention involves the modification of a single feed, two band, PIFA. The modifications that are provided by this invention enhance the dual or two band capability of prior art PIFAs, and the modifications are easy to implement. Modifications that are made to a single feed, two band, PIFA do not increase the volume or the linear dimensions of the prior art PIFAs, thus retaining the desirable compactness of a prior PIFAs.
Since PIFAs in accordance with this invention provide more than two resonant frequencies within the cellular and non-cellular bands, it is much easier to achieve a required bandwidth that is centered around the multiple resonant frequencies for three band, four or five band operation of a PIFA.
For example, in order to extend the operation of a cellular, two band, PIFA so as to include the GPS band, PIFAs in accordance with this invention require a bandwidth of only about 7.29% in PCS band, and only about 0.13% in GPS band, instead of a bandwidth of about 23.35% that is needed to cover the combined GPS/PCS bands (1575 to 1990 MHz). Similarly, in order to extend operation of a cellular, two band (GSM/DCS), PIFA in order to cover the ISM band, the bandwidth requirement for a PIFA in accordance with this invention is only about 9.47% in DCS band, and about 4.08% in ISM band, as compared to a bandwidth of about 37.52% for the combined DCS/ISM bands (1710 to 2500 MHz).
Therefore the present invention""s single feed, three, four or five band, PIFAs, that are provided by embodiments of this invention, offer the new and unusual feature of overcoming the enormity of a bandwidth requirement that is centered around any specific resonance frequency that covers two cellular frequency bands and one non-cellular frequency band.
This invention ensures that a single feed, three band, four band or five band, PIFA in accordance with the invention provides for the simultaneous coverage of multiple cellular and non cellular frequency bands, and does not require an increase in the overall volume or size of the PIFA.
This invention provides a single feed, three band, four band or five band, PIFA that is of simple construction, that is compact in size, and that is cost effective to manufacture and fabricate.